VI. THE EFFECT OF DREDGING ON THE BENTHOS 



1 . Introduction . 



There are few studies of conmiunity development in unconsolidated 

 marine sediment. Reish (1961a, 1962, 1963) observed no obvious sequence 

 of colonization in recently dredged boat harbors in southern California. 

 The principal species were present during the entire study period. 

 Sailia, Pratt, and Polgar (1972) described a general pattern of coloniza- 

 tion for the Rhode Island Sound disposal area that was similar to the dis- 

 posal area in this study. Species arrived in order of their power of dis- 

 persal. Motile animals moved in first, and within a year nonselective 

 larvae of opportunists settled. 



Migrations of animals into the dredged and the disposal areas at 

 Moss Landing were not observed. Larvae of opportunists were the first 

 to settle in the dredging and disposal areas, although at the disposal 

 station their numbers were apparently restricted by the presence of ani- 

 mals that survived the dumping. 



There is no evidence that opportunists alter or prepare the environ- 

 ment for later species. Evidence does support Connell's (1972) argument 

 that the sequence is related to life history characteristics of oppor- 

 tunists and dominants rather than site modification by pioneers. 



2 . The Control and Harbor Stations Before Dredging . 



A permanent station was located in 6 meters of water along the edge 

 of the Moss Landing Harbor entrance channel (Fig. 1) where dredging 

 occurred. The middle of the channel was not dredged in this part of the 

 harbor; the area served as a control station about 25 meters from the 

 dredged station. 



In summary, before dredging the harbor station and control were in- 

 habitated by a deposit-feeding assemblage of active, burrowing infauna. 

 The dominant species are listed in order of abundance in Table 5. 



3. Recovery of the Benthic Fauna . 



The harbor station was dredged in late August 1971. The bottom was 

 dredged 1.5 meters below its original level, exposing patches of clay 

 that were gradually covered by fine sand from the steeply cut channel 

 wall. The first postdredging sample was taken on 12 September 1971; the 

 last ones on 2 April 1972. Lateral movement of fauna into the dredged 

 area was slight and restricted to large mobile epifauna (decapods and 

 gastropods), and possible some bivalves (Peterson, 1972). 



Eighty-six percent of the total number of individuals were removed by 

 the dredging. Most of the specimens taken in September 1971 were recently 

 settled 4. bioaulata (polychaete) , and some oligochaetes . The dominant 



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